Imposter Commander Keen

The Imposter Commander Keen is a Loquax, probably brainwashed by Mortimer McMire to kill Commander Keen, (provided that the rest of Calidune didn't do so first).

From the Official Help File:

This particular Loquax believes himself to be Commander Keen. He seems less than trustworthy, but he may hold the only means of escape for our hero.

This boss monster is similar to the Loquaxes, but with one deadly exception, being that he kills Keen if he touches him. When shot, the ICK will charge in that direction for a period of time, and may stop abruptly, much to the dismay of... well, you!
This is the Nospike replacement in Dead in the Desert.